Nickel-metal hydride storage battery including negative electrode containing yttrium substituted hydrogen storage alloy and electrolyte solution containing sodium hydroxide

Abstract

A nickel-metal hydride storage battery includes a negative electrode containing a hydrogen storage alloy and an electrolyte solution. The hydrogen storage alloy has a CaCu5-type crystal structure and contains at least a Ni element and a rare earth element. The rare earth element is partly substituted with an Y element, and the electrolyte solution contains NaOH in an amount of 2.0 M or more.

What is claimed is: 
     
       1. A nickel-metal hydride storage battery comprising:
 a negative electrode containing a hydrogen storage alloy represented by the formula La (1-x-y) Y x Ce y Ni a Co c Mn b1 Al b2 , 0.05≦x≦0.4, 0.05≦y≦0.3, 4.35≦a≦4.55, 0.01≦c≦0.4, 0.1≦b1≦0.4 and 0.35≦b2≦0.45; and 
 an electrolyte solution, 
 wherein the hydrogen storage alloy has a CaCu 5 -type crystal structure, 
 wherein the electrolyte solution contains NaOH in an amount of 2.0 M or more, and 
 wherein the content of elements other than rare earth elements in the hydrogen storage alloy is 5.1 times or more than that of the rare earth elements in terms of the number of atoms. 
 
     
     
       2. The nickel-metal hydride storage battery according to claim  claim 1 , wherein the content of elements other than the rare earth elements in the hydrogen storage alloy is 5.2 times or more than that of the rare earth elements in terms of the number of atoms. 
     
     
       3. The nickel-metal hydride storage battery according to  claim 1 , wherein the content of elements other than the rare earth elements in the hydrogen storage alloy is 5.1 times or more and 5.4 times or less than that of the rare earth elements in terms of the number of atoms. 
     
     
       4. The nickel-metal hydride storage battery according to  claim 1 , wherein the content of elements other than the rare earth elements in the hydrogen storage alloy is 5.2 times or more and 5.4 times or less than that of the rare earth elements in terms of the number of atoms. 
     
     
       5. The nickel-metal hydride storage battery according to  claim 1 , wherein the electrolyte solution contains NaOH in an amount of 6.0 M or more and 8.0 M or less.